There is a thread about this somewhere on the forum that I read a while back that I have been unable to relocate. Mine does the same thing, only in low speed, using a/c or heat.
Local dealer said to clean out cage fan and clean in cabin air filter, which I did-didnt work...makes same noise.

The thread i ran across mentioned something about the fan becoming unbalanced and having to disassemble the housing and tighten the screws that hold the fan together.

I just installed an aftermarket fan I bought off Amazon. I compared the new unit to the OEM model. The main difference I notced is the shaft for the motor goes through the mount, where the OEM model stops at the bottom of the mount. The OEM one made by Delphi is made in Vietnam, where after market one is made in Taiwan. The aftermarket one appears to be as well; possibly better made than the OEM model. I have my fingers crossed and am hoping for the best for no more squeak.

Same Problem Here.. I mentioned it when I brought my truck in for the usual oil change, etc. The service guy said they would check it out. He came back and said it was a leaf in the blower. Somehow I knew he would say that. I wanted to back hand him, LOL.

They did stop the noise for about 1 day. But then it came back. Have a hard time believing that a leaf could get past the cabin filter. Surely it wouldn't happen twice within 24 hours.

Guys when I took mine off to clean it with MAF cleaner there was alot of some sort of metal powder on bottom of cover plate, Im thinking it gets in the bearings which causes it to squeal. Cleaning it out would be the best fix cause getting a new one is still the same design until toyota redesigns it or gets rid of delphi. Remember this is all my theory but it works for me.

I just installed an aftermarket fan I bought off Amazon. I compared the new unit to the OEM model. The main difference I notced is the shaft for the motor goes through the mount, where the OEM model stops at the bottom of the mount. The OEM one made by Delphi is made in Vietnam, where after market one is made in Taiwan. The aftermarket one appears to be as well; possibly better made than the OEM model. I have my fingers crossed and am hoping for the best for no more squeak.

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Keep us posted on the Taiwan fan. Mine is just starting to chirp as well.

YAY!!!!! Glad I found this mine started squeaking about a month ago. Can not wait to get this done this week just one more thing for my Taco holiday (tires & wheels, bed mat, debadge & black [them] out).